1. Field of the Invention
This invention generally relates to an optical disc recording/reproducing system and in particular to a control method and system for controlling a recording and/or reproducing operation in such an optical disc system.
2. Description of the Prior Art
In general, an optical disc, for example, of 5.25 inches can store data of up to approximately 200-800 megabytes. When storing data on such an optical disc, data are stored in a predetermined format and sector by sector as shown in FIG. 2. One sector generally includes an address section 1, a flag section 2 and a data section 3, and the data section 3 normally has a capacity to store 512-2048 bytes of data. The flag section 2 is a section for storing sector management information, such as information for indicating whether or not a particular sector is in use and whether or not processing for an alternative sector has been completed, other than the data which users wish to store. For this reason, the information stored in the flag section 2 is very important. Because, if the information indicating whether or not a particular sector is in use has been erroneously interpreted, although valid data are stored in that sector, new data are written into that sector to thereby destroy the original valid data (overwriting) unintentionally.
The detailed structure of the flag section in a sector is diagrammatically shown in FIG. 3. During recording (writing), at a predetermined timing T.sub.1 from a sync pit of preformat pit 4 which has been previously formed on an optical disc, a high power laser beam for writing information on a recording film of the optical disc irradiates the optical disc to thereby form a flag pit 5. The flag pit 5 is also a record pit and the presence or absence of this pit constitutes sector management information. During reproduction, the presence of absence of such a flag pit 5 is determined depending on whether an RF signal at a timing T.sub.1 after the sync pit 4 in a manner similar to that of the recording mode is higher or lower than a predetermined threshold level, and thus this information constitutes sector management information.
If the amplitude of the RF signal corresponding to the flag pit 5 is not sufficiently high, it may not exceed the threshold level. For example, due to fluctuations in laser power and/or defects on the surface of the optical disc, the amplitude of the RF signal corresponding to the flag pit 5 decreases. The amplitude of the flag pit 5 mainly depends on the power of the writing laser beam, and the larger the power of the writing laser beam, the higher the amplitude of the flag pit 5. Thus, it is preferable to set the power of the writing laser beam high in order to secure writing or recording of a flag pit 5. On the other hand, a record pit (not shown) in the data section 3 will have a larger amplitude if the power of writing laser beam is larger. However, if the power of laser beam is excessively increased, a pit duty ratio, i.e., a ratio between a pit length (T.sub.PIT) and a pit-to-pit length (T.sub.LAND), shifts from a desired state as shown in FIG. 4(a) to an undesired state as shown in FIG. 4(b). As a result, there can be jitter in the signal.
In accordance with the prior art approach, in order not to increase jitter during reproduction of data from the data section 3, adjustments are made to obtain appropriate recording power to produce a desired pit duty ratio as shown in FIG. 4(a), and the flat pit 5 in the flag section 2 is also recorded using the same writing power. In accordance with this approach, since the flag pit 5 is defined using the writing power which has been adjusted in relation to the pit duty ratio for the data section 3, there could arise a problem of erroneous recognition of flag information.